About Me

I am a politically-progressive, ethically-herbivorous anthropoid pursuing a paleontology education in the Los Angeles Basin. I am largely nocturnal, have rarely been photographed, and cannot thrive in captivity.

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23 November 2011

It's Curtains For The Expensive Tissue Hypothesis

From my previous post, you already know what a poor attempt at debunking the paleo diet looks like. Now, I figure I owe you an example of how to do it right. Call this a Thanksgiving present.

"Energetics and the evolution of human brain size," published earlier this month in Nature, tests and refutes the expensive tissue hypothesis. It's impressive work, and pretty devastating to the hypothesis that has provided a rhetorical foundation to the paleo diet mythology for over a decade now.

Navarrete's, et. al.'s, main findings (further details below) are:

There is no negative correlation between brain size and gut size in any mammalian taxa, refuting the ETH's prediction to the contrary;

There is, however, a strong negative correlation between brain size and adipose tissue deposits; that is, fatter animals have smaller brains than lean ones; and,

Humans are seeming exceptions to this rule because our fat deposits don't interfere adversely with our means of locomotion, thus freeing up energy for encephalization that other primates have to use for carrying around all that fat.

And the stunning thing about this paper is that the authors didn't simply test the ETH using new data, but also re-tested the data from the original paper using newer statistical methods and controlling for confounding factors that that Aiello & Wheeler missed, for whatever reason.

Their conclusion: when adiposity, phylogenetic relationships, sample bias and sex differences are controlled for, Aiello's & Wheeler's original data don't support their hypothesis any better than the newer data does! In short, the ETH is wrong at the foundation, not just at the margins.

But, you should still hold your applause for a moment, so we can make clear not only what this paper is, but also what it is not.

It is not evidence that pre-humans were strict vegans. It is not evidence that Homo sapiens are natural herbivores. It is not evidence that meat and dairy, in themselves, are intrinsically either good or bad for us. If you're the kind of vegan who looks for an evolutionary hook to hang your fall-from-grace fantasies on, you'll have to look elsewhere. Prehistoric humans and their ancestors ate meat, and sometimes a heck of a lot of it. You'll just have to deal with that.

However, the paper is pretty good evidence that meat wasn't essential to our evolution. Meat, it turns out, probably didn't make us smart, after all. At the level of vegan blogosphere debate ammo, that might be cause for some applause.

The Original Problem
To understand how the ETH came about, how thoroughly Navarrete, et. al., have undermined it, and on what grounds they have done so, it's probably a good idea to hop in the Wayback Machine and understand what Aiello & Wheeler were trying to explain in the first place.

The $64,000 question in paleoanthropology (adjusted for inflation) for the last 80 years or so has been, "why can humans have such freakishly huge brains compared to other primates their size, but still have the same basal metabolic rate?" The question is rooted in a biological principle called Kleiber's Law, which demonstrates that the metabolic rate of most animals scales to the 3/4 power of their mass; this law holds true across the animal kingdom, and appears to function in plants and bacteria, too: even within individual cells themselves! Kleiber's law can be used to precisely calculate the metabolic rate of any animal just by knowing their total mass. In short, it shows that animals of roughly the same size will have roughly the same basal metabolic rate (BMR), and that's where the problem with humans comes in.

It turns out that within an animal, the metabolic rate is not evenly distributed among all its tissues. Some tissues -- brains, hearts, lungs, livers, the GI tract, to name a few -- use more calories than others; they are thus "expensive." Every organ has its own individual metabolic rate. So, even though animals of equal size will have equal overall BMRs, they won't necessarily allocate that energy to their organs in the same way.

Let's say you have two species of roughly equal mass. One of them is characterized by a super strong heart, and the other by advanced lung capacity. Hearts and lungs both use a lot of energy, so each species will allocate its overall BMR to its distinct tissues in different ways, but will still have the same total BMR as the other. This means that without a change in overall mass, the strong-hearted species can never have the amazing lungs of the strong breather, and vice versa. Kleiber's law must hold, and to do that, some organs and tissues have to take priority over others. So long as their overall BMRs remain the same, different species of equal mass can display a lot of variation in the ways their individual tissues consume energy.

This is the crux of the human brain problem.

Using Kleiber's law, Aiello & Wheeler noted that an 80-lb. australopithecine would have had roughly the same BMR as an 80-lb. Homo sapiens, despite the difference in their brain sizes. The human brain would have 4 to 5 times the metabolic cost of the softball-sized australopith brain. So, Aiello & Wheeler reasoned, in order to maintain the BMR predicted by our mass, humans must have made a trade-off between competing tissues at some point in our evolution; i.e., as our brains gobbled up more energy, some other set of tissues had to get less, and thus shrink over evolutionary time. Something had to give.

After assessing the cost and importance of various tissues within modern humans, Aiello & Wheeler concluded that the human tissue most reduced in comparison to other primates was the GI tract. As our brains got bigger, our guts got smaller. As a result, we had to become dependent on more high-quality, nutrient-dense, easily-digested food than other primates to maintain the high cost of our brains, since our reduced guts could no longer handle the sorts of food on which our ancestors had subsisted for millions of years. They proposed that the most likely reliable source of such calories was meat and other animal products. A dramatic increase in animal matter in the hominin diet eased the energy constraints imposed by nature on big brains, and allowed our brains to grow to massive proportions without violating Kleiber's law.

In the popular press and later, in the blogosphere, the short hand version of the ETH became, "meat made us smart," or "meat-eating made us human." But that's not precisely what Aiello & Wheeler were claiming, and the difference between what they claimed and what carnists who cite them claim is crucial to understanding what Navarrete, et. al., have accomplished with their new paper.

For the ETH, meat itself wasn't really the point. Though Aiello & Wheeler proposed it as the probable source of the necessary calories, they hinted that other high-quality foods, like sugary fruits, tubers, or oil-rich nuts and seeds, could also have done the job. A close reading shows that the ETH was fundamentally about total calories, not specific calorie sources. Even so, the prominence of meat-eating in the paper supplied de facto legitimacy to several paleofantasies about the necessity of meat to the human diet, one of which would become the modern paleo-diet movement.

But more fundamental to the ETH than meat-eating -- indeed, the whole point of the paper -- was the claim that Kleiber's law is maintained through a necessary trade-off between expensive tissues within a given organism, in this case Homo sapiens. Increased meat-eating was merely a consequence of this claim, not the foundation of it. And for the last 15 years or so, the argument over whether meat was important to our evolution has obscured the more fundamental -- and eminently more testable -- claim of an expensive tissue trade-off.

Any good hypothesis can produce at least one testable prediction. And the ETH has one, right there for everyone to see (though it's been astonishingly ignored for 15 years). If the ETH is true, we should expect to find a tight negative correlation between brain mass and the mass of other expensive tissues across a range of taxa, not just among primates. And it's this prediction, not whether cavemen were meat-eaters, that Navarrete, et. al., set out to test.

The Fat Of The Matter
The key way they tested the overall hypothesis across various mammal groups was controlling for adipose tissue deposits in their calculation of a given animal's mass. In short, they omitted fat deposit mass from all specimens, eliminating it as a variable. This was an important control tactic (and one not used by Aiello & Wheeler in their original paper), because adipose mass varies by season and habitat among many species, and can thus be a major confounding variable. Only by eliminating it altogether and testing brain size against fat-free body mass, the authors reason, could a possible trade-off between tissues be reliably detected.

Under these conditions, no negative correlation between brain size and digestive tract mass was found. In fact, no negative correlation was found between brain size and the mass of any expensive tissue. The authors did, however, uncover a tight negative correlation between brain size and adipose tissue depots: the fattest species had the smallest brains.

Given Kleiber's law, this might at first look like a dilemma: fat tissue doesn't use a whole lot of energy, so why would it constrain brain size? The answer is that it costs an animal a lot of energy to lug the extra weight around, especially while climbing or running. And it's here that humans -- along with whales and seals -- have an advantage: fat stores don't significantly interfere with our ways of getting around. Bipedalism and dorso-ventral flexion (the swimming method used by cetaceans and pinnipeds) are simply more efficient ways of moving.

To understand just how big of an impact bipedalism has on human energy expenditure, take a look at the paper's Supplemental Material, and its discussion of the different energy costs that excess fat imposes on humans and chimpanzees. Human foragers spend between 18 to 22 percent of their daily energy on locomotion. Chimps have a comparable but somewhat larger range of 16 to 30 percent. But, because of the different ways they move around, a 10 percent increase in body fat deposits for humans means only a 1 percent increase in needed energy, while for chimps it means a 2 to 3 percent increase.

In other words, it costs chimps twice to three times as much energy to move around the same amount of body fat as a human. Further complicating the matter is that the energy cost of travel during climbing for primates is almost directly proportional to body mass. Quadrapedal terrestrial walking and briachiation as modes of transport simply impose higher costs on primates than does efficient bipedalism. This energy cost adds up over time (especially evolutionary time), and thus can constrain the total amount of BMR available for encephalization.Thus, because humans save so much energy by being bipedal, they can store relatively large amounts of adipose tissue and still grow big brains.

Digging Up Old Data
If Navarrete, et. al., had stopped there, they'd have a pretty strong case: the ETH's predicted negative correlation between brain size and organ mass appears not to exist, at least among mammals. But, they took their investigation a step further and decided to re-test Aiello's & Wheeler's original data set, controlled for several compounding factors that Aiello & Wheeler hadn't accounted for. And that's where the real knock-out punch to the ETH happens.

As detailed in the Supplemental Material, Aiello & Wheeler were working with a data set that had a couple of problems. Namely, it was biased towards catarrhine primates over platyrrhines; it didn't control for sex differences between members of species with marked sexual dimorphism (sexual size dimorphism affects body mass more than brain size), or for differences in the body mass of wild vs. captive specimens of the same species; and it didn't account for phylogenetic relationships between various hominid species (a fact I have pointed out before).

In fairness to Aiello & Wheeler, most of this was beyond their control. 15 years ago, for instance, we didn't know that Paranthropus was a sister taxa to Homo rather than a direct ancestor, and the literature on primate body masses simply didn't contain as wide a sampling of platyrrhines as it does today. Aiello & Wheeler did the best they could with what they had.

Nevertheless, Navarrete, et. al., were able to identify and control for these confounders in a new test using the latest phylogenetic statistical methods on the original data sample. And the results did not support Aiello's & Wheeler's hypothesis; even their own data failed the ETH in the end.

Taken together with the new author's own data, these re-testing results pretty much have put the ETH down for the count. If they want to save it, Aiello & Wheeler will have to tackle Navarrete, et. al., with much more rigorous data and analysis than they used the first time around. Make no mistake, this is a quiet revolution in action.

What this means to the vegan blogosphere is that there is now a robust and scientifically credible argument against the claim that meat-eating was essential to our evolution... and the case has nothing to do with animal rights or other aspects of vegan ethics. That being said, this paper cannot and should not be used as evidence that hominins did not eat meat at all, or that pre-human ancestors were purely frugivorous. If we do that with this paper, we'll be just as guilty of building a paleofantasy as the caveman dieters were when they turned the ETH into their shibboleth.

So, while you're dining on Tofurkey or some African pumpkin stew (my planned Thanksgiving meal) this holiday, and obnoxious Uncle Carnist breaks out the old meat-made-us-human canard for the millionth time, feel free to take him to the mat. He's had it coming for years.

47 comments:

Thanks for this! I enjoyed it so much I read it aloud to my boyfriend. I'm part of a crossfit affiliate and so surrounded by paleo-dieters quite often. This will be nice to have in my arsenal when I'm asked why I'm not in on the crossfitters' diet of choice.

National Geographic had a detailed analysis of Itzi, the 5000 year old ice man. Probably the only stone age man whose stomach contents have been analyzed. It was meat and grain. No doubt meat provides high energy and protein, but they also found that Itzi would probably have died within ten years of heart attack or stroke. He was about 45 years old, so was having the same problems Americans are having with their high meat diet. Nobody says those ancient heavy meat eaters lived long and healthy lives. "The China Study" proves that diets heavy in meat and diary is killing us.

We know that grains by themselves don't cause heart disease, because populations that subsist on them, such as Chinese and Japanese, and for that matter most of the world's traditional populations that haven't switched to a modern diet, do not suffer from heart disease, while Westerners do.

We also know that Paleolithic people did consume grains, and in fact modern day hunter gatherers consume them as well. I give you links that prove it. Therefore, the whole Paleo assumption that "grains aren't Paleo" is total and complete BS.

i believe you are not correct on any of the above accounts - but i really do not want to argue here -

that paleolithic people or hunter gatherers ate "grains" or "bread" as a recent headlines touted, is summarily wrong - of the 9 (7 or 9 i believe) organic particles found on the 20K+ old grindstone were either roots, tubers or rhizomes with only 1 being an old pseudo-grain. NOTHING like modern grains and bread. the chinese and japanese also in now way "subsist" on "grains" but rather have historically eaten rice often along with fish, meat and vegetables - the fish eating populations being the healthiest - the chinese health is deteriorating rapidly in recent decades due to the switch from nominally healthy rice to devastatingly unhealthy wheat. and please don't quote to me the hugely biased "results" of the China Study until you consider Denise Mingers superb dismantling of ol Doc Campbells self-interested unscientific tripe.

I would suggest to you the writings of a REAL PRACTISING doctor (ol doc campbell never saw a patient) - one who actually treated thousands of patients using lo carb diets for a lifetime practice curing almost every chronic condition he came across - an austrian named Dr Wolfgang Lutz - and his book "Leben Ohne Brot" - Life Without Bread--

as far as your links - nature magazine is questionable at best and don matesz has gone off the deepest of ends after denouncing paleo - his formerly lucid writings have deteriorated into frothy-mouth vegetarian/vegan rantings of the most absurd kind.

and by now you have guessed - i ascribe to a primal/paleo diet outlook so any more discussions between us is probably quite pointless.

"most of the world's traditional populations that haven't switched to a modern diet,"

The modern diet is considerably more carbohydrate, especially grain, heavy. Lets not forget eskimos living on a 100% animal based diet.

There's simply not a single example of a "traditional" society that did not at least attempt to make animal protein a large percentage of their diet.

Yes, humans have a lot of dietary flexibility, but thats exactly what makes us such a successful species. If you hadn't eaten for a week you would try to eat anything, including grains, even if they poisoned you.

Modern grains are also modified to be easier to process, and are considerably lower in actual nutrient content. This is done to make them more profitable, not better to eat. Grains our ancestors tried to live on would have been processed in a different way (probably fermented? possibly sprouted? It's hard to say of course), but you cannot in any way compare it.

I guess in the same way you can't compare modern meat practices with hunting (ie, the idea of paleo re-enactment is stupid and pointless), the animals are not the same and they don't eat the "correct" foods.

Veganism has *only* the moral ground. From a metabolic viewpoint it is really a fruitless argument. We simply do not gain enough energy/ protein from plants themselves to make them the "ideal" staple in our diet, with the exception of highly processed, questionably food items. Ever tried raw veganism? You have to eat a loooooooooooot to make it work. (Thats an interesting debate too; the volume of food one needs to eat to get adequate nutrition on a vegan diet relative to the population we have)

I'm not even trying to make a counterpoint to veganism as a moral viewpoint, let me make that clear; you are simply wrong about human nutrition.

Over thousands of years our digestion and metabolism may (and probably will, thanks to our excessive population) alter to gain more actual nutrition from plant foods, but I imagine it would be at a cost to something else, likely our brains.

Oh yeah, regarding heart disease?

http://www.sciencedaily.com/releases/2009/06/090625133215.htm

I think the issue in the western world is the focus on eating non-food, high carbohydrate items. Additionally, there is a huge focus on eating vegetable oils over saturated fats (even plant based saturated fats are frowned upon, eg palm oil). Finally in addition to the high - GI diet that the western world prescribes, it is still possible to eat a lot of reasonable fats, and this combination is the problem.

As your body becomes more inflamed due to excess sugar, indigestible food like grains etc, fats that your body has little ability to break down... your body is simply not fed things that it can rebuild itself with.

Great post. This is pretty damning evidence against the "meat made us smart" concept. Unfortunately it's also equally damning against Richard Wrangham's "cooked tubers made us smart" idea as well, which I was quite fond of :)

Anonymous,

The stomach content only confirmed the last couple of meals before Otzi's demise.

Hair analysis suggests that Otzi's overall diet was almost completely vegan. Was this addressed by National Geographic? See 32:40 in McDougall's talk:http://www.youtube.com/watch?v=4XVf36nwraw

Interestingly, McDougall chose not to mention Otzi's (poor) health and dental state. I think it's far-fetched to say that Otzi's poor health was due to meat. If anything, it might have been excessive reliance on einkorn wheat.

By the way, the data from The China Study is all correlational. It really shouldn't be considered "proof" of anything, let alone the idea that meat is harmful.

My name is Ben Chasteen and I am the Science/Technology editor at Before It's News, a people-powered news site serving over 4 million people a month. We publish over 4,000 user-generated posts each day at BeforeItsNews.com.

I contacted months ago to see if you wanted to syndicate your RSS feed however, but didn't hear anything back. This time I am contacting you because I was wondering if you would be interested in receiving a short email of our top 5 Science/Technology stories each week? We have a lot of stories that the mainstream media don't cover. I think you'd find it a great source of unique information. If it's ok, please just email me back with a YES. You have my iron-clad promise that your email address will not be used for any other purpose or be added to any mailing lists.

I would also be your personal contact at Before It's News, should you ever have questions or need anything.

By the way, we also offer free WordPress blog hosting, and we can syndicate your RSS feed, if you're interested. Just let me know.

Thank you for this, Humane Hominid! You go the meaning of our article exactly right and explain it very well. Just one little addition: Even if we would NOT control for the amount of fat storage, the ETH would be rejected, as then the correlation between gut mass and brain size would even be positive within mammals, and within primates.

Thanks for your kind words, and for visiting. It's gratifying to know I'm getting some things right, after all. :)

Sarah,Ha ha, you should read it out loud to your CrossFit pals, too. Or maybe just print and post it on the bulletin board.

Will,Otzi's last meal was red deer meat and possibly cereals; his second to last meal was ibex meat, some dicot plants, and possibly cereals. -- http://www.pnas.org/content/99/20/12594.long

The claim of his veganism based on hair sample analysis was found to be questionable, at best. All evidence indicates that he was a life-long omnivore.http://rstb.royalsocietypublishing.org/content/355/1404/1843.full.pdf+html

If Otzi was eating vegan for most of his life (maybe) and then for reasons of scarcity he ate meat and grains, it could be preciselly that he was living tough times.If fruits and veggies were his main food why would he eat meat and grains (so tough to hunt, eat and digest) unless there was some scarcity?When you are in vacation at the beach, what do you enjoy the most?I do enjoy fruits, salades, coconut water and meat, avocados etc. of course when I have them available.

Thanks for the post. This post was passed to me by a Vegan friend of mine (as we are debating the health virtues of paleo va vegan)

If the homosapiens were evolved with big brains not because we ate meat but for some other reason, then the fact remains that human have always eaten meat. This would suggest it is important for our health.

Again I'm not saying it's essential to eat meat for good health but I don't trust that medical science understand food and nutrition that well (maybe they understand it 50% say) And for that reason being vegan raises the risk of missing out nutritionally because you dont know what you dont know.

In addition on the actual point that humans need to eat meat for large brains. I do think its interesting that all the most intelligent animals on the planet are carnivores or omnivores.

HumanwhalesdolphinsdogsAll apes & Chimps (they do eat meat as well)

Many animals classified as Herbivores (folivores) also eat meatA site that outlines the complex eating habits of apes and chimps can be found herehttp://beyondveg.com/billings-t/comp-anat/comp-anat-2a.shtml#categ not strict

No, the fact that humans have always eaten meat does not suggest that it is important to our health. It might suggest that meat-eating provided human ancestors with a marginal advantage over competitors that improved reproductive fitness. This isn't the same thing as "being important to our health," though. Lots of such adaptations come with profound negative trade-offs (witness: sickle-cell anemia).

In other words, meat could have helped us survive and still have been bad for us at the same time.

Most wild animals are, it's true, functional omnivores to some degree. This is actually evidence against your position, as such an ancient trait is unlikely to evolutionarily significant in hominids. To show that it was significant or necessary, you'd have to do a lot more than simply point out its existence. That's only the beginning of an analysis, not the end of one.

I disagree with your assumption "No, the fact that humans have always eaten meat does not suggest that it is important to our health. ". There is evidence that the whole Homo genus have eaten meat that is (depending on your source) around 2 million years of meat eating. This is a consistent attribute of the human species. It cannot be compared with a transient genetic mutation such as sickle-cell anemia.

On your second point "Most wild animals are, it's true, functional omnivores to some degree. This is actually evidence against your position, as such an ancient trait is unlikely to evolutionarily significant in hominids."

Personally I am on the fence as to wether eating meat is a cause or effect of larger brains but it definatly seems to be related (whales, apes,dolphins ect all omnivore / carniviour) and it is true that brains are extremely nutrient dense and the human brain takes up 25% of our waking energy according to wikipedia http://en.wikipedia.org/wiki/Brain. So I can see logically how eating meat in a pre industrial society could help as in the wild its a very energy dense food. That said nowadays (with our supermarkets) you could eat a bag of now sugar and get alot of energy quite easily.

However a bag of sugar will not contain the same nutritional make up as that of of an animal tissue. For me the health issues today stem around nutrition not energy. The records show that paleolithic man was generally very healthy so eating meat worked then. My issue with veganism or vegetarianism is that moving to a diet that does not include meat requires an understanding of what we are missing nutritionally from the meat. I do not believe that medical science understands that topic sufficiently and therefore you are likely to miss something.

The first part is not an assumption, it's an observation. A history of meat-eating does not suggest that meat-eating is important to our health. Natural selection doesn't care how healthy you are. It just wants you to make sure your kids survive to reproduce. If meat-eating gives you a slight advantage in that task, then it will be preserved, even if it is bad for you from a health perspective. That was the point of the comparison to sickle-cell anemia. Adaptive advantages always come with negative trade-offs.

And you missed my second point completely. If meat-eating is something we share in common with other primates, then it wasn't definitive to our own evolution. This is not an opinion, it's how evolution works.

Producing a list of traits proves nothing. You have to demonstrate whether the trait in question is ancestral or derived. If ancestral (that is, shared with so many other previous species that it's nothing special), then it's not helpful to your case. If derived (that is, unique to one taxon, or to a small handful of taxa sharing a common ancestor), then it's potentially important to your case.

So, if you mean to suggest that omnivory is a derived rather than ancestral trait of H. sapiens (or cetaceans, for that matter), you're gonna need to present some darn impressive evidence. If you don't understand what I just said, then you don't understand basic evolutionary biology, and really ought to stop citing it to justify your diet philosophy.

Anonymus,The purpose of good health is the thrival and personal evolution including the growth in consciousness of the individual.If you think we as human beings, we are on earth just to make babies, we are not in the same paradigm.Even agriculture had an important role in the evolution of human beings and the "materialistc consciousness" but that civilization was at the expense of individual health (meaning, joyful, vigorous, long lasting wellbeing and consciousness of our spiritual nature).So, as Paul said, a trait that may help increase the population of certain species (like a pest) doesn't necesarily imply a betterment of individual health (whole wellbeing)Did I well understood you Paul?Otherwise, look at those countries were life expentacy is very short but they make lots of babies so the species will not extinct.It makes me think about temporary abundance of predators that will then self balance with the environment as in our case that we are spoiling the earth and pay the consequenses sooner or later.I'm my personal experience, being raw vegan for 11 years, I am thriving and my brain is working at it's best without any meat, grain or cooked food.Not only that, I haven't eat meat for longer than that, 28 years, just that I was still eating cooked for 17 years before switching to more paleolithical eating.Think about it.Of course I speak from experiance and I don't see why would our ancestors have needed meat or fire to ""individually thrive"".I perceive there has been a devolution of health for the sake of the human experience but that as individuals, were are not obliged to go in that same direction of physical and mental degeneration, trapped as domesticated animals spoiling the earth and being accomplices of suffering.

This is my first post to your blog and I must say I found your posts surprisingly lucid for a vegan advocate. I actually think most your posts are pretty spot on, but I did want to point out a big problem with your reply to Paul on January 29, 2012 5:08 PM. It is a mistake many vegans unconsciously make due to their classification of all omnivory as basically the same in the sense that it isn't vegan.

Actually omnivory in humans is both a derived and an ancestral trait of H. sapiens. For example our basic teeth are an ancestral trait of insectivory species that changed over time as we evolved to add fruit and later other foods in our diet. Insects are "animals" to a vegan, but the derived traits H. sapiens has to chase down and kill an antelope have nothing to do with the ancestral traits we have for insectivory. By the same token the derived trait we have for eating starchy foods (an extra abundance of Amylase in our saliva compared to other primates) has nothing to do with the ancestral frugivorous traits. Yet to a vegan whether it is a fruit or a tuber makes little difference. Both are plant foods.

So when you said, "So, if you mean to suggest that omnivory is a derived rather than ancestral trait of H. sapiens", you made a meaningless statement. H. sapien's specific type of omnivory has a wide variety and blend of both ancestral and derived traits.

Part 1/2I like your article. The only issue which is not clear to me is whether the Kleiber's law applies after removing the fat mass or before it. If it applies before it then Navarette et al, changed the whole basis of the ETH.

Lets go on a tangent.Lets just talk about physics using Kleiber's law.

Efood is the energy in the food that we eat.

Ewaste is the energy that leaves the digestive tract.

Egut is the energy that food digestion uses, including the upkeep of the digestion system.

Einput = Efood - Ewaste; Energy that was made available by the digestive system.Eoutput is the Energy that is made available to the rest of the system, not including the gut.Egut = Einput - Eoutput.

Note my definition of Egut is different from ETH's treatment of gut size.

Einput is the complete energy used by the system.

Einput = Egut + Ebrain + Erest.

Now Kleiber's law states that Energy remains constant for an animal.

ETH says that Erest is more or less constant across homonids. I would think the same args will apply to other species also. Similar brain, heart, etc. Fat is a confounding factor :-).

If this is true that Erest is more or less same across species, then we can simplify it to.

Assuming that Erest is constant, brain size is inversely proportional to the ratio of energy utilized by the gut.

In other words brain size is directly proportional to Energy efficiency of the Gut.

The only point of contention in all of this is that Erest is not much variable. Looking at the energy utilization of each tissue, you see that compared to the brain and neurons the rest consumes very little. The only big consumer other than that is gut. So I am not sure why Erest will not be nearly constant.

Ofcourse this assumes that Kleiber's law is based on the animal as a whole and does not depend on removal of the fat. I have never heard of that thing though. I just think that Navarette et al changed the whole basis of ETH, maybe they didn't understand ETH properly.

Lets just think about it in physical terms.How do you get a high gut efficiency?

By eating things from which energy can be extracted easily. Things that are very easy to get energy from are sugars, non-resistant Starches, and fat. Rest of all are difficult to get at. For fiber and resistant starches we need bacteria which involves a lot more expense, and for protein we need to convert it to glucose to obtain the energy, which is very thermogenic.

One thing is for sure. Cooking makes energy a lot more easily available from food. The gut changes in Homo Erectus are very noticeable. So Wrangham's thesis is not in danger even if ETH goes out the window.

I am not sure what navarette et al are getting at, but the concept of ETH makes a lot of sense. If you look in the above terms you will see why Herbivores (too much bacterial requirement) have smaller brains, compared to Carnivores (too much protein to glucose conversion), and omnivores (somewhere in between) have bigger brains than carnivores. It just makes sense.

I agree with you meat is immaterial, although brains and bone marrow was critical in human evolution. That is the most easily available large source of fat. Humanoids did spend a large part of the evolution as scavengers.

IMO the evolution went like this.1) Fruits provided simple sugars to early primates.2) Hunting provided some meat and importantly some fat, which may have allowed brain growth. I am not so sure though.3) Scavanging for brain and bone marrow. This would be the critical point.4) Tools allowing better hunting, easier access to fat.5) Cooking even better access to fat, and now access to easily digestible starches.6) Amylase enzyme growth, allowing less reliance on bacteria for extracting energy from starches.

Wrangham's hypothesis makes it difficult to reconcile step5 and 6, as now they happened very much apart 1.8mya to 200kya. I guess this can only be solved if plants were not very starchy before 200kya, and humans were instrumental in selecting and propagating starchy plants. If that is the case something like agriculture started 200kya. Possibly why sorghum starch was found on neanderthal teeth.

I sometimes think that maybe coconut played a large role in our evolution. Lots of easily available fat and sugars. Very very good for us. Large fruit plentiful in africa where we evolved. Although the fruit requires tools to get at, so does not get rid of the scavenger phase. The scavenger phase was before they started using tools.

2/2Obviously I am an omnivore, and don't side with either the vegans or the so called carnivores.

Fat and starch both, are good for health. Not so much protein or fiber, although a little of both (10-15%) is required :-). But micro-nutrients are the real kings. Avoiding toxins is critical. I follow the PerfectHealthDiet.

Anonymous #umpteen asked: What is the purpose of good health if not increasing the chances of survival and reproduction for the individual and the group?

Depends what you mean by "good health." Evolution is a system built around the adequate, not the optimal. Most organisms who survive to reproductive age are already adequately "healthy" enough to make babies. As long as that's the case, nature doesn't care if they're unhealthy in other ways (got a gene that promotes cholesterolemia, sickle cell anemia or schizophrenisa? Tough shit, you're good enough to make babies, and that's all evolution cares about).

"Also, you don't get to change the ETH's parameters in order to save it"

I'm no expert in biological science, but in physics hypotheses and theories have their parameters modified or even added and subtracted all the time. When Einstein added in the parameter of the cosmological constant in 1917 to General Relativity, GR could have been more considered a hypothesis not a theory, as its predictions had not been experimentally tested (perihelion precession of Mercury had been observed long before GR).http://en.wikipedia.org/wiki/Cosmological_constant

I'll concede this much, praguestepchild: I shouldn't have used the word "parameters." I should have said "foundation." What these authors have done isn't simply highlight a flaw in the periphery of the ETH, but demonstrated that it is completely wrong in its fundamental claim. There is no negative correlation between brain size and gut size, or between brain size and the size of any other expensive tissue.

Nitpick: The precession of Mercury's perihelion had been observed prior to GR, but it wasn't explained. In fact, it can't be explained with Newtonian gravitation alone, but GR does explain it. So Mercury's perihelion was a good early test of GR. Other things (such as gravitational lensing) also provided nice tests for GR and it still works reasonably well except at small scales (then it breaks down).

The cosmological constant was added because Einstein's field equation worked out with an expanding universe and at the time, the universe was thought to be static so he basically went "oh, I must be missing something here" and tacked on a constant to fix things. He later called this his greatest mistake when the universe was found to be expanding, but now that we think the universe is accelerating, this constant (or a new theory of gravitation) is probably necessary.

I definitely wouldn't say that one famous example indicates that physicists add and remove parameters from equations "all the time" either.

" they hinted that other high-quality foods, like sugary fruits, tubers, or oil-rich nuts and seeds, could also have done the job."

Yes. But you're missing the key point - animal fat is the most nutrient dense fuel. Yes, it is possible that humans could have evolved in this way, but unlikely since it would require, effectively, farming to ensure continual access to foods.

Lets be generous and assume that paleolithic tubers have the same amounts of calories as a modern potato, and somehow magically also contain more micronutrients. (I'll also ignore essential fatty acids and the old B vitamin bugbear).

You're talking, say, 200 calories from a single potato. So in order to survive, the 80 lb human has to find, what, 8 per day? Every day. And remember, humans/pre humans were definitely social animals.. so the number of these tubers need to be found in considerably greater numbers....

I'm not denying that "it's possible that a large brain can grow without meat", sure. But show me an intelligent herbivore, or frugivore. Eating the fat and organs of an animal provides a huge amount of calories and nutrition immediately, which is why predators exist in the first place; its opportunistic eating.

It's not a stupid argument that you make, but it's not very strong. Language (and indeed, even being able to recognise that other humans can understand you) had to evolve first as a survival tool, and you don't need to coordinate to find potatoes, you just look.

You need to work on your reading comprehension skills. This is not article arguing that cavemen were vegetarians, or that tubers fueled brain evolution. It's an article arguing that the whole idea that diet of any kind fueled brain evolution is unsupported by current evidence.

And BTW, like most other paleodieters, you're getting the brain-meat hypothesis wrong. If reading Aeillo's and Wheeler's original paper is too much, I'll spell it out for you. Their hypothesis goes like this:

1) Nature selected for larger brains in hominids.2) These larges brains placed a greater energy demand on said hominids.3) Hominid anatomy, at the same time, imposed an energy constraint that would normally prevent this brain enlargement.4) Nature compensated by selecting, in turn, for hominids who spent less energy on other tissues, freeing it up for the brain.5) This reduction in energy use in (they hypothesize) the gut led to a reduction in gut mass.6) This gut reduction + brain enlargement led hominids to seek more calorie dense foods, including more meat-eating than previous hominids.

Now, if you pay attention to that sequence, you will see that bigger brains came before increased meat-eating, not after it.

Hi. I still don´t understand Navarette study (maybe because my english is not perfect). What actually change with ETH? Human still have larger brain and shorter gut than for example monkey. Okay, after subtracting fat, human has higher BMR. Possibly for brain needs, but gut is not same like has monkey, it is smaller. How can disappear correlation between energy needs of brain and gut after subtracting fat? Then brain must have even bigger numbers in comparison with fat-free body, because his energy needs doesn´t change. Can you help me understand that? Thanks :)

I'm late to this party, but have to comment. This statement of yours says it all: "However, the paper is pretty good evidence that meat wasn't essential to our evolution." I've been saying this for decades. Yes, our very early ancestors ate meat. Some of them probably even hunted for it. But, our biology didn't require either the eating of meat or the hunting of it in order to evolve into our modern form, or to ensure our survival. I'm a vegan and my fat butt, big brain, and little gut do just fine on nuts and berries and leaves and grass. That'd be coconuts, avocados, blueberries, spinach, and green onions. Nobody is starving at my house.